Components, in particular sensors (e.g. for safety harnesses), are fastened to a vehicle in different ways in the automobile industry. Typically, fastening types such as screwing, riveting and gluing are used. Especially in case of sensors used in safety-critical applications, such as air bag systems, it is crucial that these be securely mounted. On the one hand, it must be ensured that the sensor is properly mounted when the vehicle leaves the factory. On the other, the sensor must continue to be mounted in the correct place and position or be exchangeable without compromising safety in case of repair or the like during the entire service life.
For this reason, the installation process of conventional sensors, which are e.g. screw-fastened, is documented in many cases. This can be done e.g. by monitoring and recording the torque and the angle of rotation during the screwing process.
The publication DE 199 23 985 A1 discloses a sensor assembly where the housing of an air pressure sensor used to sense side impacts is fastened to a wall in the vehicle by means of fastening means, for example screws. The door of said vehicle preferably has a dual structure comprising a dry compartment next to the interior of the vehicle, a wet compartment facing the external sheet metal covering and a separating wall in between. The air pressure sensor is arranged on said separating wall. It must sense air pressure changes in the wet compartment while its electrical components or at least the plugs and wires are arranged in the electrically safe dry compartment.
For this purpose, the separating wall has an opening through which either the air pressure is transferred to a so-called dry compartment sensor, which is arranged in the dry compartment, or the plug portion of a wet compartment sensor, which is arranged in the wet compartment, extends into the dry compartment. At the same time, the opening in the separating wall is closed by pressing the fastening element against said wall.
DE 10 2006 059 034 B3 describes a method for attaching a component to a wall, wherein an insertion tab of said component is first inserted in the wall and then a snap-in hook of the component is pressed into the opening in the wall via an inclined plane during a tilting movement towards the wall until said snap-in hook engages behind the wall. Such a method has the drawback that much pressure is applied to the insertion tab during said tilting movement and part of the sealing effect is lost when the hook engages, which means that the pressure exerted before must be so high that the seal may be partly destroyed during the tilting movement.
A generic method and a corresponding fastening device are for example known from DE 10 2008 048 318. Instead of a screwed connection, said method comprises a solution based on a bayonet mount, wherein a retaining element comprising at least one, preferably at least two, retaining wings is arranged in a support element so as to be rotatable therein, and said retaining wings can be inserted in the opening in the wall in a first rotational position, are turned about an axis of rotation that is at right angles to the wall and engage behind the wall in the second rotational position, thus fastening the support element, the retaining element and the assembly thereon to the wall. This allows for tool-free and fast, yet secure mounting. One or more support lugs on the support element can prevent said support element from turning along during rotation, and an additional locking unit can prevent the retaining element from turning back once it has reached a predefined position, for example the desired final position. The retaining wing(s) comprise(s) portions of different thickness in the radially outward direction. In conjunction with a suitably adapted inner radius of the hole geometry, the degree of pressure with which the fastening device is pressed against the wall can now be corrected according to the specific wall thickness. In case of a thick wall, a large radius of the hole geometry is selected and the radially outward, narrow portions of the retaining wing are used while the thicker inner portions extend into the inner radius of the hole geometry. In case of a thin wall, a smaller radius is selected and the thicker inner portions are used, thus achieving a thickness that compensates for the thinner wall thickness so that the degree of pressure against the wall is approximately the same. However, said portions have the same thickness along a radius. In addition, much pressure must be applied to the support element during rotation to allow the retaining means to engage behind the wall. If additional manual pressure is no longer applied, the degree of pressure against the wall will reduce.
The support element is provided with a sealing element which seals the opening in the wall in a fluid-tight manner. Such a mounting solution, however, requires rotation of the retaining element and the bayonet element relative to each other, which means that there must be a suitable play between the two elements. It is difficult to ensure that no moisture will enter said play, at least during extreme temperatures and throughout the long service life required. If there is no such play, the seal is subjected to a considerable degree of friction during rotation about the central axis of the component, abrasion may occur or the seal may even turn out of position, thus becoming leaky.